THE ROYAL MINT GREAT BRITAIN NATIONS OF THE CROWN 3 COIN TRIAL PIECE SET The Royal Mint Ultimate Trial Coin Set (3 Rare top pop graded NGC Trial Coins in cherry wood box) A boxed premium set, with 3 stunning coins graded by NGC as top pop, none out there graded finer, One Amazing talking piece with one a rare error coin included.. In this set All Three trial coins have been graded by NGC as "Top Pop" The finest examples in the wild to date, The 2014 trial coin in this set as well as being graded on a rare error label, has been double struck this is when a coin is struck and then fails to be fully ejected from between the dies before being struck a second time with the strike off-centre, coupled with a partial collar, This is when the planchet (blank piece of metal) is struck between the dies, it is at the same time surrounded by a retaining collar which ensures the resulting coin is perfectly shaped. For coins with edge milling the collar also features a negative ridged structure to impart the ridges (millings) onto the edge. It all happens very quickly. If a planchet isn't positioned properly within the collar it results in an odd edge.Sometimes a raised lip, either partially or all the way around the coin or a smooth section of the rim where it should feature milling.